The present invention relates generally to an acrylic compound. This invention also relates to the use of these compounds, for example, as monomers that can be homopolymerized or copolymerized with other monomers to make resins within sub-200 nanometer (nm) photoresist compositions.
Photoresists are photosensitive films that are used for the transfer of images to a substrate. In a typical lithography process, a substrate is generally coated with either a positive or negative photoresist coating. The photoresist-coated substrate is then exposed through a photomask to an activating radiation source which transfers the pattern of the photomask onto the photoresist-coated substrate. Depending upon whether the photoresist coating is positive or negative, the radiation source either increases or decreases its solubility in a subsequently applied, alkaline developer solution. In a positive photoresist coating, the areas masked from the radiation source remain after development while the exposed areas are dissolved away whereas in a negative photoresist coating the opposite occurs. The patterned photoresist image acts as a mask for subsequent substrate patterning processes such as etching, doping, and/or coating with metals, other semiconductor materials, or insulating materials.
Current interest in the semiconductor industry has increased in photoresists that can be photoimaged with short wavelength radiation, i.e., exposure radiation of about 200 nm or less such as 193 nm (ArF laser) or 157 nm (F2 excimer beam laser) wavelengths. Short exposure wavelengths may allow for the formation of smaller features within the semiconductor device. In this connection, a photoresist that can provide well-resolved images after exposure to a 193 nm or 157 nm wavelength radiation source may allow for the formation of relatively smaller (e.g., sub-0.25 μm) features. Smaller device features meet the industry demands for smaller dimension circuit patterns and provide for greater circuit density and enhanced device performance.
Photoresist materials, particularly sub-200 nm materials, are particularly challenging to develop because of the need to balance a variety of different performance characteristics. Photoresist materials should ideally provide high transparency at the exposure wavelength, sufficient resistance to plasma-etching processes, and functional groups that are capable of undergoing sufficient photochemical transformations that change the solubility in developer solutions. Besides these, other important characteristics include, but are not limited to, reasonably simple synthesis procedures, adhesion to the underlying substrate, glass transition temperatures compatible with typical processing temperatures, acceptable shelf storage lifetime, and minimum toxicological risk.
The prior art discloses a variety of monomers that can be polymerized and used as base resins within photoresist compositions for sub-200 nm applications. For the higher end of this range (e.g. 193 nm), cycloaliphatic structures have drawn the most attention. For lower wavelength applications (e.g. 157 nm), the monomers tend to have one or more electron-withdrawing groups such as fluorine or hydroxyl and one or more cyclic structures. It is believed that the combination of the electron-withdrawing groups and the one or more cyclic structures improve the performance of the photoresist composition, particularly transparency. For example, U.S. Patent Application US2002/0004570 (“Zampini I”) describes photoresist compositions that contain polymerized units of cyclic olefin monomers having one or more pendant cyclic electron-withdrawing groups. The pendant cyclic electron-withdrawing groups disclosed may be N-based, O-based, or S-based.
European published patent application WO 02/21214 (“Zampini II”) discloses base resins within 157 nm photoresist compositions that contain at least one electronegative group that includes aromatic groups such as phenolic moieties. In this connection, Zampini II specifically describes vinyl ether entities that incorporate fluorinated aromatic structures as the electronegative group.
European published patent application WO 02/21213 (“Taylor”) describes resins that are used within photoresist compositions that contain photoacid-labile deblocking groups substituted with one or more electron-withdrawing groups. The electron-withdrawing moieties within the resin are bonded to the blocking group so that the acid-catalyzed blocking and deblocking reactions are relatively unaffected by their presence.
Japanese Application JP 2002/179,731 (Chemical Abstracts 137:54625; “Harada I”) discloses photoresist resins that contain the structure: CO2CR1R2R where R1 and R2=H, F, or a C1-20 alkyl and R=C3-20 cyclic alkyl. In addition, Harada I describes an acrylate resin that contains fluorinated alkyl groups in ester side chains.
U.S. Patent Application 2002/0051936 (“Harada II”) describes an acrylic resin that contains repeating units containing a fluorinated hydrocarbon group, an acid labile group, and an adhesive group. Harada II describes one of the units, preferably the acid labile group, as having at least one alicyclic structure. Harada II also describes acrylic polymers containing the structure —O—C(R1R2)—C(H)(R3)R4, where R1, R2, R3, and R4 are H, F, or an unsubstituted or fluorinated, straight, branched or cyclic alkyl group.
European Application EP 1 126 322 describes resins for use in a 157 nm photoresist that contain fluorinated ester groups.
European Application EP 1,103,856 (“Tsutsumi”) describes a fluorine-containing resin that contains polymerized units of an acrylic or methacrylic acid ester wherein the ester moiety comprises a fluorine-containing group. Tsutsumi further describes moieties where the fluorine-containing group has a cyclic structure such as a fluorine-containing benzene ring, a fluorine-containing cyclopentane ring, a fluorine-containing cyclohexane ring, or a fluorine-containing cycloheptane ring.
Photoresist materials currently being developed for 157 nm, such as the materials described above, are difficult to prepare and raw materials are often difficult to work with or not readily available. For example, it is quite common to utilize hexafluoroacetone (HFA) for incorporating hexafluoro-2-propanol groups into the monomers. The hexafluoro-2-propanol groups, which incorporate strong electron-withdrawing groups such as fluorine atoms and hydroxyl groups, offer improved transparency of the materials at that wavelength when compared to its non-fluorinated analogs. Despite its advantages in transparency, hexafluoroacetone itself is a highly toxic gas and may not be readily available as a raw material. Further, other issues, such as selectivity and low yields associated with current manufacturing processes for making these compounds, may make it less practical and cost effective to use HFA-based monomers within photoresist compositions.
An alternative to using a HFA-based monomer within the photoresist material is using a trifluoroacetone-based monomer such as the cyclic trimer; 4,6-dihydroxy-2-methyl-2,4,6-trifluoromethyltetrahydropyran. Current procedures for making the cyclic trimer; 4,6-dihydroxy-2-methyl-2,4,6-trifluoromethyltetrahydropyran cannot be readily adapted to a large scale commercial production. These procedures include the reaction of trifluoroacetone with reactive metals such as sodium (A. L. Henne and P. E. Hinkamp, J. Am. Chem. Soc. 76, 5147, 1954), magnesium-amalgam (S. Resconich, Ph. D. Thesis, Purdue University, 1961), fused potassium hydroxide (D. H. Campbell, Ph. D. Thesis, Purdue University, 1955), chlorohydrin in the presence of potassium carbonate (H. E. Simmons and D. W. Wiley, J. Am. Chem. Soc. 82, 2288, 1960), and anhydrous diethylamine or dipropylamine (M. M. Dhingra and K. R. Tatta, Org. Mag. Res 9 (1), 23, 1977).
Accordingly, there is a need in the art to provide resins polymerized from monomers that are transparent at sub-200nm wavelengths. There is also a need in the art for safe and cost effective industrial processes to make fluorine-containing acrylic monomers at greater yields, less cycle time, lower process temperatures, less volatility, and less toxicity.
All references cited herein are incorporated herein by reference in their entirety.